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Puget Sound in Washington State has been damaged by “hotspots” of acidified seawater. Derrick Coetzee; Wikimedia Commons

Ocean acidification, a problem usually associated with global greenhouse gas emissions, is also caused by coastal pollution and other local sources that can be managed under existing laws, according to a research team led by the Center for Ocean Solutions at Stanford University.

In a report published in the May 27 edition of the journal Science, a team of marine scientists and legal experts provided the first roadmap for local communities to combat ocean acidification by applying federal and state laws and policies – from the U.S. Clean Water Act to municipal zoning regulations.

Harmful impacts

Studies point to carbon dioxide emissions as the primary reason why the ocean has become more acidic in recent decades. "As the level of atmospheric carbon dioxide continues to rise, so too does the amount of CO2 in the ocean, which increases the ocean's acidity," the authors explained. "[But] freshwater inputs, pollutants and soil erosion can acidify coastal waters at substantially higher rates than atmospheric CO2 alone."

Rod Searcey

Melissa Foley

Seawater acidification reduces the ability of marine creatures to create shells and skeletons, harming everything from commercial oyster beds to coral reefs, the authors said. They cited Puget Sound, Chesapeake Bay and other coastal regions where livelihoods and lifestyles have been damaged by acidic "hotspots" – patches of ocean water with significantly depressed pH levels. The lower the pH, the more acidic the water. Coastal waters have a pH budget that can be pushed beyond its spending limits when local and atmospheric sources of acidity are combined, the authors said.

"Since an acidification hotspot can negatively impact a community, its causes need to be tackled quickly," said co-lead author Melissa Foley, a science early career fellow at the Center for Ocean Solutions. "We identified practical steps communities can take today to counter local sources of acidity."

Solutions

Few jurisdictions have taken steps to mitigate acidification, according to the report. "The alignment of a localized ecological harm with a local policy solution is rare," said co-lead author Ryan Kelly, an analyst for science, law and policy at the center.

To address the problem in the United States, the researchers recommended that coastal communities first turn to the federal Clean Water Act, which directs state governments "to ensure that precipitation runoff and associated pollutants [which can increase acidification] are monitored, limited and consistent with the sustainable functioning of aquatic ecosystems."

To comply with the act, seaside communities can reduce runoff by implementing stormwater surge prevention and coastal buffer zones, maintaining intact wetlands and improving water treatment, the authors said. "In many cases, federal funding is available to help local governments complete these kinds of projects," they wrote.

Ryan Kelly

The authors also recommended controlling coastal erosion – "a classic function of local and state governments and one that could markedly benefit coastal ecosystems by reducing nutrient and sediment loading of water," they wrote. "Such coastal inputs may be enriched with fertilizers and, if unchecked, can further increase acidification in estuaries and coastal waterways."

Other recommendations included the adoption of local zoning policies that reduce runoff and carbon dioxide emissions, along with enforcement of existing federal emissions limits on pollutants such as nitrogen oxide and sulfur oxide, which can contribute to local acidification.

EPA example

A recent lawsuit against the Environmental Protection Agency (EPA) demonstrates how existing laws could be applied to the problem of ocean acidification, the authors said. In a memorandum required by the settlement, the EPA emphasized that states should identify waters that are impaired due to declining pH levels and track them over the long term.

"Using pH levels as a type of 'master variable' helps judge the cumulative impact of a variety of pollutants that are flushed into the ocean by coastal communities," Foley said. "This is important to understanding the magnitude of a water quality problem."

Although much of the report focused on U.S. policies, the researchers noted that similar legal tools exist in other countries to guard against local causes of ocean acidification.